This invention relates to a rotary light tester for inspecting empty cans for defects, and in particular for continuously inspecting empty cans for various defects such as a pinhole and cracks without damaging the cans. Such defects generally result in leakage and occur in the manufacturing line for drawing and ironing can bodies (DI can) of a two-piece can.
This kind of inspection of an empty DI can has heretofore been performed after coating or printing of the inner and outer surface thereof to prevent corrosion and decorate the can after the trimming operation which shears the open end to a fixed finish height Then the necking and flange is formed on the open end. Therefore the amount of transit light in a pinhole of 100.mu. diameter or below covered with coatings or print inks has been reduced to that in a pinhole of about 10.mu. diameter. The amount of transit light in a pinhole of 20.mu. diameters or below cannot be detected with any detection accuracy. Accordingly the detection of very small pinholes is very difficult. Also the accurate detection of defective cans is very difficult owing to the luminuous intensity of the transit light which becomes much less weak upon reaching the light detector with the inner coating film affecting the absorbing attenuation action of the reflective scattered light respectively.
This conventional pinhole detection apparatus is known in U.S. Pat. No. 3,416,659. According to a schematic representation of FIG. 1, a flange opening end (10a) of the DI can (10) tightly contacts a light seal plate (14) of a dark box (12) with the DI can (10) standed upside down. The box (12) has a window (12a) and communicates with the interior of the can (10) through the window (12a). A vacuum pump (not shown) reduces the internal pressure of the box (12) and the can (10) through an exhaust opening (16) provided in a side wall of the box (12), resulting in a difference between the internal and the atmospheric pressure. The can end tightly contacts the flange opening end (10a) of the can (10) with the light seal plate (14). The light seal plate (14) is opaque rubber packing. The bite of the flange opening end (10a) in the light seal plate seals light. The can (10) has light sources (18) around itself and receives both the direct light from the sources (18) and the reflected light from a cylindrical reflector (20) around the source. A photo detector (22) provided within the dark box (12) detects irradiated light through the can (10) from the light sources (18) and then converts irradiated light into an electrical output (24) through a signal circuit (not shown), so that pinholes in the can are found.
According to the conventional apparatus of FIG. 1, light from the light sources (18) passing through the pinhole into the interior of the can (10) reaches the photo detector (22) directly or reaches it with light repeatedly scattered and reflected within the inside wall of the can (10). The photo detector (22) is capable of detecting pinholes anywhere in the can (10) by the optical integral action of reflected, scattered light, and possibly acquires the high sensitive pinhole detection action.
However, in this conventional apparatus, light leakage out of the seal portion between the flange opening end (10a) of the can (10) and the light seal plate (14) produces detection noise. To reduce the amount of light leakage, reduced internal pressure is provided within the box (12) and the can (10) is made to tightly contact the flange opening end (10a) with the light seal plate (14). As a result, wear of the light seal plate (14) become extreme. Generally, in the conventional apparatus, the can (10) receives the light detection action with the condition that the flange is formed in the flange opening end (10a), in other words, the end surface of the flange opening end (10a) is rounded. But even with this roundness the flange opening end (10a) results in extreme wear of the conventional light seal plate (14) of rubber packing. In general, a side use of two to three weeks and both sides use of about six weeks results in frequent replacements of the parts, and makes maintenance of the detection apparatus difficult. In addition, the use of the easily worn light seal plate (14) results in error detection.
Also, in the conventional apparatus, in the same way as regards the air pressure method, coatings or print inks cover pinholes on the inside and outside surfaces of the can. Especially, detecting pinholes of 100.mu. diameter or less becomes extremely difficult. Practically, a can having pinholes covered with coatings or print inks keeps good air tightness for only a few days. But, in most cases, pinholes produce leakage after a week and remarkably increase the ratio of defective cans. In particular, the defective cans having substances have a practical influence on common consumers. This is a very big problem.
As will be apparent from the above description, it is better to detect pinholes before the coating or printing. But as is well known, in the DI processing operations, the ironing and drawing processed DI can has a necking and flange processing in the opening end. The shape of bright cans remains as it was before the flange processing is made. The trimmed end surface has a width of about 0.17 mm, which is very thin. As a result, when the opening end (10a) tightly contacts the light seal plate (14), the light seal plate (14) has remarkable wear or is easily damaged in a particular case. Therefore, it is impossible to detect pinholes before coating or printing.
Can pinhole detection apparatus described in Japanese Patent Public Disclosure No. 50-48983 and U.S. Pat. No. 3,750,877 and Utility Public Disclosure No. 53-118685 adopt a gasket of opaque material of rubber substances which is the same as the material of the light seal plate (14) of FIG. 1, and consists of a feed star wheel disposed in an empty can supply station, a central star wheel feeding empty cans from the supply station into a light detection station and a discharge star wheel which receives tested cans from the central star wheel located between a defective can discharge station and a good can discharge station. The mechanism and structure of such apparatus is large. In the discharge of good cans, the cans are mechanically held by a yoke opened and closed with actuation of a cam mechanism, and released to the discharge star wheel by actuation of the cam opening the yoke when the held cans come into the good can discharge station. In the discharge of defective cans, cans are mechanically held by the yoke and released by another cam action opening the yoke with a solenoid operation receiving a delay command signal. Thus, holding empty cans by the yoke easily produces holding scars on an outer surface of the empty can and may deteriorate the quality of the cans. Further it is difficult to maintain and check the apparatus.
An apparatus for optically inspecting can bodies, which is described in Japanese Patent Public Disclosure No. 53-12682, (U.S. Pat. No. 4,074,890) adopts elastic forming plastic having an inward -shaped section, such as a hermetical ring of neoprene or urethane instead of the light seal plate (14) of FIG. 1. In the window (12a) of the box (12) of FIG. 1, a window glass of transparent acrylic resin is hermetically disposed. When the empty can (10) come into the light detection station, the action of atmospheric pressure on the hermetical ring hermetically closes light by pushing the flange (10a) of the can (10) with one piece of the ring on the side of the opening end of the can (10). Therefore, it is inevitable to use the air actuator. It makes the structure mechanically complicated. The position of the flange opening end of the can to the hermetical ring must be strictly determined. If not, leakage of air pressure breaks the light-tightness and produces error judgements, as does abrasion of the hermetical ring. In addition, the air push of a piece of the hermetical ring to the can flange substantially covers the flange end. Hence it is impossible to optically detect cracks of the flange opening end.
The instant invention, therefore, has as an object to provide a rotary light tester for continuously inspecting empty cans which improves defect detection as compared to conventional apparatus.
The object of this invention is to provide a rotary light tester for continuously inspecting empty cans in which the inspection is made on empty cans just after being passed from the trimming work.
Another object of this invention is to provide a rotary light tester for continuously inspecting empty cans in which the inspection is made on bright empty cans before the inner and outer surfaces of the cans are coated or printed.
Another object of this invention is to provide a rotary light tester for continuously inspecting empty cans in which the inspection is made on empty cans before being fed into the necking and the flanging operation.
A further object of this invention is to provide a rotary light tester for continuously inspecting empty cans which makes it possible to precisely detect defective cans without attenuating transit light into the interior of the empty can.
A further object of this invention is to provide a rotary light tester for continuously inspecting empty cans which is supplied with a wear resisting light seal circular plate which is easily maintained and which has a long replacement life.
A further object of this invention is to provide a rotary light tester for continuously inspecting empty cans which is supplied with a light seal circular plate making easy insertion of the opening end of the can.
A still further object of this invention is to provide a rotary light tester for continuously inspecting empty cans which is supplied with a light seal plate which is a circular plate making it easy to coaxially settle the center position of the opening end.
A still further object of this invention is to provide a rotary light tester for continuously inspecting empty cans which is supplied with a light seal circular plate having a groove to insert the opening end of the can therein and being of a material harder than that of the can.
A still further object of this invention is to provide a rotary light tester for continuously inspecting empty cans which is supplied with a light seal circular plate having a groove which is specifically formed to further provide reflective attenuation of outer invasion light.
A still further object of this invention is to provide a rotary light tester for continuously inspecting empty cans which is supplied with a light seal circular plate having a surface which is especially useful to further reflective attenuation of outer invasion of light.
An additional object of this invention is to provide a rotary light tester for continuously inspecting empty cans which is supplied with a star wheel making it smooth to slide freely and receive and discharge cans to a can receiving seat setting empty cans.
An additional object of this invention is to provide a rotary light tester for continuously inspecting empty cans which makes it possible to detect pinholes of 25.mu. diameter or below with high accuracy.
The above and other advantages of the invention will become more apparent in the following description and the accompanying drawings.